。
She's not a good conversationalist.
Literal
She [topic-は] conversation [subject-が] unskillful is.
The pattern 話が下手 uses が to mark the skill area for the na-adjective 下手 (へた, 'unskillful/bad at'). Like 上手 and 好き, these evaluative na-adjectives treat their object as a grammatical subject. The polite copula です keeps the register neutral.